added more docs for product and related models
added more docs for product and related models

Parisson/cartridge,syaiful6/cartridge,syaiful6/cartridge,viaregio/cartridge,traxxas/cartridge,Kniyl/cartridge,wyzex/cartridge,wyzex/cartridge,viaregio/cartridge,dsanders11/cartridge,traxxas/cartridge,wbtuomela/cartridge,wyzex/cartridge,Parisson/cartridge,Parisson/cartridge,ryneeverett/cartridge,jaywink/cartridge-reservable,Kniyl/cartridge,dsanders11/cartridge,traxxas/cartridge,dsanders11/cartridge,syaiful6/cartridge,ryneeverett/cartridge,wbtuomela/cartridge,stephenmcd/cartridge,jaywink/cartridge-reservable,ryneeverett/cartridge,Kniyl/cartridge,jaywink/cartridge-reservable,stephenmcd/cartridge,wbtuomela/cartridge,stephenmcd/cartridge